Selenium vacancy-regulated (Ni,Co)Se₂ nanosheets with accelerated carrier separation for high electrochemical...

The design of porous nanosheets using vacancy engineering together with structural modulation engineering is an effective way to realize high energy density supercapacitors. However, the effects of vacancies on electronic structure, carrier density, and electrochemical activity have not yet been fully explored and elucidated. Herein, we used ZIF-L as a precursor to prepare triangular pyramid-shaped (Ni,Co)Se₂ nanosheets rich in selenium vacancies. This method involved the utilization of the ZIF-L transformation technique. Porous nanosheets have been demonstrated to facilitate electrolyte ion transport and ensure efficient redox processes even at higher currents. The BET analysis indicates that the presence of selenium vacancies leads to an increase in the specific surface area, thereby facilitating the exposure of active sites. Furthermore, density functional theory calculations, UV-vis spectroscopy, and Mott-Schottky plots demonstrate that selenium vacancies narrow the bandgap of (Ni,Co)Se₂ and enhance carrier density. Furthermore, the results of DOS suggest that the presence of vacancies contributes to improved material conductivity. As a result, V_Se-(Ni,Co)Se₂ possesses an extraordinarily high specific capacity of 1011C g^-1 at 1 A g^-1_, together with a capacity decay of only 25.8 % even at 10 A g^-1. In particular, a hybrid supercapacitor assembled using activated carbon and V_Se-(Ni,Co)Se₂ possess excellent energy density (68.13 Wh kg^-1) at a power density of 750 W kg^-1. This work opens a new way to obtain hybrid supercapacitor cell-based materials based on ZIF conversion.